Lsrs At The Mpls Core - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Chapter 39 Configuring MPLS QoS

LSRs at the MPLS Core

This section provides information about MPLS QoS features for LSRs at the core (MPLS-to-MPLS) for
MPLS and MPLS VPN networks. Ingress features, egress interface, and PFC3B features for Carrier
Supporting Carrier (CsC) QoS features are similar to those used with MPLS to MPLS described in the
next section. A difference between CsC and MPLS to MPLS is that with CsC labels can be imposed
inside the MPLS domain.
MPLS to MPLS
MPLS QoS at the MPLS core supports the following:
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The following section provides information about MPLS-to-MPLS PFC3B mode MPLS QoS
classification. Additionally, the section provides information about the capabilities provided by the
ingress and egress modules.
Classification for MPLS-to-MPLS
For received MPLS packets, the PFC3B ignores the port trust state, the ingress CoS, and any policy-map
trust commands. Instead, the PFC3B trusts the EXP value in the topmost label.
The MPLS QoS ingress and egress policies for MPLS traffic classify traffic on the EXP value in the
Note
received topmost label when you enter the match mpls experimental command.
MPLS QoS maps the EXP value to the internal DSCP using the EXP-to-DSCP global map. What the
PFC3B does next depends on whether it is swapping labels, imposing a new label, or popping a label:
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Per-EXP policing based on a service policy
Copying the input topmost EXP value into the newly imposed EXP value
Optional EXP mutation (changing of EXP values on an interface edge between two neighboring
MPLS domains) on the egress boundary between MPLS domains
Microflow policing based on individual label flows for a particular EXP value
Optional propagation of topmost EXP value into the underlying EXP value when popping the
topmost label from a multi-label stack.
Swapping labels—When swapping labels, the PFC3B preserves the EXP value in the received
topmost label and copies it to the EXP value in the outgoing topmost label. The PFC3B assigns the
egress CoS using the internal DSCP-to-CoS global map. If the DSCP global maps are consistent,
then the egress CoS is based on the EXP in the outgoing topmost label.
The PFC3B can mark down out-of-profile traffic using the police command's exceed and violate
actions. It does not mark in-profile traffic, so the conform action must be transmitted and the set
command cannot be used. If the PFC3B is performing a markdown, it uses the internal DSCP as an
index into the internal DSCP markdown map. The PFC3B maps the result of the internal DSCP
markdown to an EXP value using the internal DSCP-to-EXP global map. The PFC3B rewrites the
new EXP value to the topmost outgoing label and does not copy the new EXP value to the other
labels in the stack. The PFC3B assigns the egress CoS using the internal DSCP-to-CoS global map.
If the DSCP maps are consistent, then the egress CoS is based on the EXP value in the topmost
outgoing label.
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
Understanding MPLS QoS
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